Toxic dispersants in Gulf oil spill creating hidden marine crisis

Toxic dispersants in Gulf oil spill creating hidden marine crisis

Tom Levitt and Nicole Edmison

6th September, 2010

More than 200 million tons of crude oil have gushed into the Gulf of Mexico since the rupture of Deepwater Horizon. The chemicals used to clean up the spill have received less attention but could have devastating long-term effects on the marine ecosystem

Nearly two million gallons of controversial oil dispersants have been applied to the waters of the Gulf in an attempt to break up the spill – by far the largest use of such chemicals in history.

Oil dispersants are composed of two main ingredients: solvents and surfactants. With the aid of wave action, solvents work to reduce the surface tension of slicks, breaking the oil into droplets so the surfactants can penetrate the mass more deeply. 

Surfactants quickly work to coat the outside of the droplets to prevent them clumping together again. Very small drops of oil are then capable of moving away from the surface of the water and dispersing throughout the water column. 

However, this process of dispersing oil neither eliminates nor decreases its toxicity. In fact it creates a much more toxic cocktail of oil and chemical dispersant. Experts say this cocktail mix is now beginning a slow but sure degradation of the ecosystem from the bottom up. Despite this environmental officials in the US have allowed them to be used on an unprecedented scale.

Tiny droplets of combined oil and dispersant adhere to plankton, says Dr Susan Shaw, founder and director of the Marine Environmental Research Institute (MERI). The plankton-eaters then indiscriminately gobble up the tainted particles while fish-eaters consume the poisoned plankton eaters, and so on through the marine food web.

Close links to oil industry

Two main dispersants have been in use in the Gulf of Mexico since late April. Corexit 9527 was used until supplies ran out, to be replaced with Corexit 9500. Both are products of Nalco Energy Services LP, whose board of directors is made up of former and current BP, Exxon, Monsanto and Lockheed executives. Nalco is a corporate affiliate of BP.

Questions were asked of Corexit 9527’s toxicity following its use in the cleanup of the Exxon Valdez oil spill, with cleanup workers reportedly suffered health problems, including blood in their urine, as well as kidney and liver disorders linked to 2-Butoxyethanol, the main ingredient of Corexit 9527.

On 20 May the US Environmental Protection Agency (EPA) sent BP a directive: to choose a less toxic dispersant from an approved list on the National Contingency Plan Product Schedule. Of the 18 different dispersants on the list, five were found to be less toxic, more effective and in reasonable supply. Two were found in a laboratory setting to be 100 per cent effective at dispersing Southern Louisiana crude oil.

In contrast, Corexit 9527 and Corexit 9500 are respectively 63.4 per cent and 54.7 per cent effective but BP continued to use them, arguing that they were the only dispersants in reasonable supply.

A history of damage

This is not the first time the use of chemical dispersants has been questioned.

The use of dispersants in the Exxon Valdez spill in 1989, the worst oil spill in US history before the Gulf of Mexico disaster, has been linked to the decimation of native kelp and barnacle populations in the near-shore environments of Prince William Sound. 

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